Both D1 and D5 receptors are expressed in pyramidal neurons of the cortex, including the prefrontal cortex and anterior cingulate cortex. In contrast, the D5 receptor is mainly expressed in the hippocampus, the lateral mammillary nucleus, and parafascicular nucleus of the thalamus. The D1 receptor mainly distributes in the striatum, nucleus accumbens (NAc), olfactory tubercle, hypothalamus, and thalamus. The dopamine receptors distribute differentially in the brain. In addition, D1 and D5 receptors share very high homology in their transmembrane domains, while D2, D3, and D4 receptors are closely related with highly conversed transmembrane sequences. The D1-like receptor family includes D1 and D5 receptors, while the D2-like receptor family includes D2, D3, and D4 receptors. These dopamine receptors have differing pharmacological, biochemical, and physiological functions. Dopamine receptors include D1-like and D2-like receptors. Most of them are involved in the ascending pathways, and a few of them are related to descending pathways. There are several dopaminergic cell groups from A8 to A16 that distribute in different areas of the brain. The ventral side of the mesencephalon contributes to 90% of the dopaminergic neurons. Most dopaminergic neuron cell groups are derived from a single embryological cell group that originates at the mesencephalic–diencephalic junction. ĭopaminergic neurons mainly originate from the midbrain, including the ventral tegmental area (VTA), substantia nigra (SN), and hypothalamus. Low frequency tonic firing in dopaminergic neurons is mainly related to the selection of habitual motor programs independent of reward, while high frequency phasic bursts of action potential in dopaminergic neurons are related to a reward seeking movement. The dopaminergic neuron firing patterns correlate with different behaviors. Dopamine is stored in the vesicles that are released into the synaptic cleft, which is controlled by phasic and tonic transmission. As a monoamine neurotransmitter, synthesis of dopamine is limited by tyrosine hydroxylase. In other words, some of our wants are non-conscious.Dopamine is derived from its precursor named L-3, 4-dihydroxyphenylalanine (L-DOPA), which is converted into dopamine by aromatic amino acid decarboxylase. It is important to note that these biological computations don’t always make it to our stream of consciousness. The hypothalamus controls our drives such as sex, food, and sleep, our hormonal system (via intimate connections with the pituitary gland) and aspects of the autonomic nervous system such as the sympathetic nervous system. Then, the ventral striatum summarizes all this information and sends it to the hypothalamus. The amygdala provides information about the emotional intensity of the situation and the hippocampus provides past memories that convince us to go for it. This system receives important information from the amygdala, and the hippocampus. When this system is activated, motivation to pursue a stimulus increases. Push this "wanting" system to the maximum and you get addictive behaviors. This area facilitates wanting and pursuing desired behaviors. Fortunately, both systems make social interactions worth the risk.īuried underneath the logical cortex is a structure called the "nucleus accumbens" in the ventral striatum. Of course, we are also motivated by things we enjoy doing, which would activate the ‘like’ pathway. Thus, we can be motivated by things that we want but don’t like, which would activate the ‘want’ brain pathway. In all of these examples, we are motivated to complete these tasks, but might not enjoy them. For example, a mother might have to interrupt her night sleep every two hours to feed her infant, a student might have to laboriously study for an exam, a night-person might have to wake up at 6 a.m. Most of us want what we like, but these different pathways in the brain suggest that want is separate from liking or pleasure. They are represented in separate networks (although overlapping) and involve different neurochemicals 1. These are the "wanting" and "liking" components of motivation. It has gotten really proficient at this task and has paved multiple pathways to ignite us to keep going. Our brains, moment by moment support this journey by dedicating some of its limited landscape to processing reward and motivation.
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